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Chapter 7 Review iClicker Questions and PPT Notes
Terms in this set (55)
Why does ADP have less potential energy than ATP? (iclicker)
It has two phosphate groups.
How might an inhibitor inhibit an enzyme without binding to the active site? (clicker)
Through non-competitive inhibition.
You notice that a chemical reaction in your system is happening at at slow rate. You want to speed up the reaction. What do you do? (iclicker)
Add an enzyme.
Cellular Respiration Stages
Glycolysis, Acetyl-CoA, Citric acid cycle, Oxidative phosphorylation
What happens in the cellular respiration stage of Glycolysis?
Glucose is partially broken down and a modest amount of energy is released. Fatty acids and amino acids may also be broken down by different pathways. This takes place in the cytoplasm.
What happens in the cellular respiration stage of Acetyl-CoA synethsis?
Pyruvate, produced from the breakdown of glucose in glycolysis, is converted to acetyl-CoA and CO2. This takes place in the mitochondria.
What happens in the cellular respiration stage of Citric acid cycle?
Acetyl-CoA is broken down, releasing more CO2, a modest amount of energy, and electron carriers. This takes place in the mitochondria.
What happens in the cellular respiration stage of Oxidative phosphorylation?
The electron carriers from stages 1−3 release their high-energy electrons to the electron-transport chain to produce ATP. This takes place in the mitochondria.
In the breakdown of glucose, glucose is oxidized to carbon dioxide and oxygen is reduced to water.
C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy
Loss of electrons/decrease in electron density.
Gain of electrons/increase in electron density.
How does oxidation work?
The carbon atoms of glucose are bound to other carbon atoms, hydrogen atoms, and oxygen atoms. Where carbon is bound to carbon or carbon is bound to hydrogen, the electrons are shared equally between the two atoms. But in CO2, they are not shared equally. The oxygen atom is more electronegative than the carbon atoms, so the electrons that are shared between them spend more time near the oxygen.
As a result, carbon atoms have partially lost electrons to oxygen atoms. The carbon atoms have been oxidized.
How does reduction work?
To understand the reduction reaction, we look at oxygen gas and water. In O2, the electrons are shared equally between the two oxygen atoms.
In water, the oxygen atom is more electronegative than the hydrogen atoms, so the electrons spend more time near the oxygen atom. The electron density around the oxygen atom has increased—that is, the oxygen atom has gained electrons. The oxygen atom is thus reduced.
Because it gains electrons, the oxygen atom is the electron acceptor, and because it oxidizes the glucose, it can be called the oxidizing agent.
Glucose is the electron donor and is considered the reducing agent.
LEO Goes GER
Loss of Electron is Oxidation - goes - Gain of and Electron is Reduction
At a glance, how does the oxidation-reduction reaction help?
Drives many of the processes and is ableto maintain the "flow".
Is the oxidation-reduction reaction an anabolic or catabolic reaction?
It's a catabolic reaction, it takes a large molecule and breaks it down into small units.
Where is Chemical energy stored in?
Reduced molecules like carbohydrates and lipids.
Carbohydrates and lipids have high potential energy because...
...the electrons shared in bonds are far from the nuclei of the atoms in the bond.
The energy in carbohydrates and lipids is released gradually in a series of reactions. Because glucose is oxidized slowly in a controlled manner, the chemical energy stored in glucose can be harnessed in the chemical bonds of other molecules such as ATP and electron carriers.
Two important electron carriers in cells are ______ and ______.
1. NAD+ (oxidized form) / NADH (reduced form)
2. FADH (oxidized form)/FADH2 (reduced form)
In the course of glycolysis, acetyl-Co synthesis, and the citric acid cycle, the oxidized form accepts electrons and becomes reduced. The reduced form has high potential energy, used to synthesize ATP in the final stage of cellular respiration.
During cellular respiration, the cell can produce ATP in two ways:
1. Substrate level phosphorylation
2. Oxidative phosphorylation
Substrate Level Phosphorylation
a phosphorylated organic molecule transfers a phosphate group to ADP to produce ATP; however, only a small amount of ATP is generated this way. Substrate phosphorylation occurs during stages 1 (glycolysis) and 3 (the citric acid cycle) of cellular respiration.
Most ATP is produced by oxidative phosphorylation, in stage 4 of cellular respiration.
Glycolysis is a series of how many chemical reactions?
Ten; and it can be divided into three phases.
What happens during Glycolysis?
The starting molecule for glycolysis is the six-carbon molecule glucose, and its end product is a 3-carbon molecule, pyruvate. Two pyruvate molecules are produced for each glucose molecule that enters the pathway. This process is anaerobic, as oxygen is not consumed in the process.
Phase 1 of Glycolysis.
Glucose is prepared for the next two phases by the addition of two phosphate groups, producing fructose 1,6-bisphosphate. This process requires an input of energy in the form of two molecules of ATP.
The phosphorylation of glucose traps the molecule inside the cell and destabilizes it so that it is ready for phase 2.
Phase 2 of Glycolysis.
Fructose 1,6-bisphosphate is cleaved into two molecules: glyceraldehyde 3-phosphate and its isomer dihydroxyacetone phosphate. The latter is then converted into another molecule of glyceraldehyde 3-phosphate, resulting in two molecules of glyceraldehyde 3-phosphate at the end of phase 2.
Phase 3 of Glycolysis.
Two molecules of pyruvate are formed and two molecules of the electron carrier NADH are produced. Four molecules of ATP are produced.
At the end of glycolysis:
Four molecules of ATP are produced in phase 3 of glycolysis, but two are consumed in phase 1. So the net production of ATP from a single molecule of glucose is two ATP.
Two NADH molecule are produced in phase 3.
Stages _ through _ of cellular respiration take place in the mitochondria.
A mitochondrion has an inner and an outer membrane that define two spaces. The space between the two membranes is called the _____ membrane space, and the space inside the inner membrane is the mitochondrial ______.
When does Acetyl-CoA synthesis take place?
In the presence of oxygen, pyruvate can be further broken down to release more energy. First, it is converted to acetyl-CoA and then it is further broken down in the citric acid cycle.
What happens during Acetyl-CoA synthesis?
The pyruvate from glycolysis is transported into the mitochondrial matrix of mitrochondria, where it is converted to acetyl-CoA.
Detailed explanation of Acetyl-Coa synthesis.
First, the pyruvate is oxidized to form CO2 and an acetyl group. The acetyl group is then transferred to coenzyme A, which carries the acetyl group to the citric acid cycle. These reactions are catalyzed by a group of enzymes called the pyruvate dehydrogenase complex.
One molecule of pyruvate produces one CO2 molecule, one molecule of NADH, and one molecule of acetyl-CoA. Remember that at the end of glycolysis, we had two molecules of pyruvate, so at the end of this process we have two molecules of CO2, two molecules of NADH, and two molecules of acetyl-CoA for each glucose molecule.
Citric Acid Cycle
It is also known as the Krebs cycle or the TCA cycle. During this stage of cellular respiration, the fuel molecules are complete oxidized. The chemical energy in the bonds of acetyl-CoA is transferred to ATP by substrate level phosphorylation and to the electron carriers NADH and FADH2.
Where does the citric acid cycle take place?
It takes place in the mitochondrial matrix. It is a set of eight reactions and is called a cycle because the starting molecule oxaloacetate is regenerated at the end.
Organic Molecules from the Citric Acid Cycle
Some bacteria run the citric acid cycle in reverse, incorporating CO2 into organic molecules instead of liberating it. Running the cycle in reverse requires energy, which is supplied by sunlight or chemical reactions.
The benefit to running the cycle in reverse is the generation of organic molecules produced from the cycle's intermediates.
Example of organic molecules from the Citric Acid Cycle
Pyruvate can be modified to form alanine and other sugars; oxaloacetate can form aspartate, different amino acids, and pyrimidine bases; acetyl-CoA can be modified to form acetate, which is the starting point for the synthesis of the cell's lipids; and α-ketogluterate can be modified to form other amino acids and purine bases.
Acetyl-CoA is completely oxidized and it results in; 2 ATP, 6 NADH, and 2 FADH2
The first reaction of this cycle produces a 6-carbon molecule of citrate, and the final product of the cycle is a 4-carbon molecule of oxaloacetate. The two carbon atoms that are lost along with the CO2 produced from the conversion of pyruvate to acetyl-CoA are the sources of CO2 that we exhale when we breathe.
The oxidation of carbon atoms to produce CO2 in reactions 3 and 4 is coupled with the reduction of the electron carrier NAD+ to NADH. Additional electron carriers are reduced at reactions 6 and 8.
Reaction 5 is a substrate-level phosphorylation reaction that generates GTP.
Electron Transport Chain 1
The electron transport chain (ETC) is located in the mitochondrial inner membrane. Electrons then enter the ETC via either complex I or II depending on whether they enter as NADH or FADH2. Electrons are passed from electron donors to acceptors until they reach the final electron acceptor, oxygen. When oxygen accepts the electron, it is reduced to water.
Electron Transport Chain 2
Electrons must be transported between the four complexes of the ETC. Coenzyme Q or ubiquinone accepts electrons from both complexes I and II. In doing so, it is reduced to CoQH2, which diffuses in the inner membrane, docks, and transfers electrons to complex III. Complex III transfers electrons to cytochrome c. When cytochrome c accepts an electron, it is reduced, diffuses in the membrane, and interacts with complex IV.
Electron Trainsport Chain 3
Energy is released as the electrons are passed from the high-energy-electron carriers NADH and FADH2 to the final low-energy acceptor, oxygen. Some of this energy is used to reduce the next carrier in the chain, but in complexes I, III, and IV it is also used to pump protons, and the end result is an accumulation of protons in the intermembrane space.
Due to the proton pumping of the electron transport chain, protons have a high concentration in the intermembrane space and a low concentration in the mitochondrial matrix. Protons would diffuse back into the matrix because of the gradient difference, but they cannot because they cannot pass through the selectively permeable membrane. As a result, the proton concentration gradient contains high potential energy.
For the potential energy of the proton gradient to be released, there must be an opening in the membrane for the protons to flow through. Protons in the intermembrane space are able to diffuse down their electrical and concentration gradients through a transmembrane protein channel into the mitochondrial matrix.
The movement of protons through protein channels is coupled with the synthesis of ATP. The coupling is made possible by ATP synthase.
ATP synthase has two distinct subunits called F0 and F1.
F0 forms the channel in the inner mitochondrial membrane through which protons flow. F1 is the catalytic unit that synthesizes ATP. Protons flowing through the channel make it possible for the enzyme to synthesize ATP.
Proton flow through the F0 channel causes it to rotate, converting the energy of the proton gradient into mechanical rotational energy, a form of kinetic energy. The rotation of the F0 subunit leads to rotation of the F1 subunit in the mitochondrial matrix. The rotation of the F1 subunit in turn causes conformational changes that allow it to catalyze the synthesis of ATP from ADP and Pi.
What glycolysis product is transported into the mitochondria?
What is the final electron acceptor in the electron transport chain?
The flow of energy in cellular respiration:
The complete oxidation of glucose forms 32 molecules of ATP.
The energy of glucose is released slowly in a series of reactions and captured in chemical form.
Some energy is released by substrate level phosphorylation, and some is generated through redox reactions that transfer energy to electron carriers NADH and FADH2.
These carriers donate electrons to the electron transport chain. That energy is used to pump protons across the inner membrane of the mitochondria.
The energy of the electron carriers is thus transformed into energy stored in a proton electrochemical gradient.
ATP synthase then converts the energy of the proton gradient to rotational energy, which drives the synthesis of ATP.
Pyruvate, the end product of glycolysis, can be used in many metabolic pathways. In the absence of oxygen, it is broken down by fermentation.
Lactic acid fermentation occurs in animals and bacteria. Here, electrons from NADH are transferred to pyruvate to produce lactic acid and NAD+.
Ethanol fermentation occurs in plants and fungi. Here, pyruvate releases carbon dioxide to form acetaldehyde, and electrons from NADH are transferred to acetaldehyde to produce ethanol and NAD+.
In both types of fermentation, NADH is oxidized to NAD+, but since neither molecule is produced or lost in the process, they do not appear in the overall chemical reaction.
Evolution of ETC and Oxidative Phosphorylation
Before the presence of atmospheric oxygen, the earliest organisms likely used one of the fermentation pathways to generate the ATP necessary to power cellular processes.
Cellular respiration involves an electron transport chain that creates a proton gradient that powers the synthesis of ATP. Cellular respiration can occur in the absence of oxygen, but needs a final electron acceptor such as nitrate or sulfate. Respiration in the absence of oxygen is known as anaerobic respiration and occurs today in some bacteria. The electron transport chain in these bacteria is located in the plasma membrane, not in an internal membrane.
An intriguing possibility for how this system might have evolved is that in early prokaryotes pumps were used to drive protons out of the cell in response to an increasingly acidic environment. Some pumps might have used the energy of ATP to pump protons, while others used electron transport proteins to pump protons (left).
At some point, proton pumps powered by electron transport might have become efficient enough that the protons could pass back through the ATP-driven pumps, running them in reverse to synthesize ATP (right).
The evolution of cellular respiration illustrates that evolution often works in a stepwise fashion, building on what is already present. In this case, aerobic respiration picked up where anaerobic respiration left off, making it possible to harness more energy from organic molecules to power the work of the cell.
Excess glucose is stored in two forms: as starch in plants and glycogen in animals.
Both of these molecules are large branched polymers of glucose.
Glycogen is stored in muscle cells and liver cells. When stored in muscle cells, it is used to provide ATP for muscle contraction. The liver stores glycogen for the whole body, releasing it when it is needed elsewhere.
Glucose molecules at the end of glycogen chains can be cleaved one at a time in the form of glucose 1-phosphate, which is then converted into glucose 6-phosphate, the intermediate in glycolysis.
How Other Sugars Contribute to Glycolysis
A variety of carbohydrates are digested, producing a variety of disaccharides or monosaccharides. In some cases, glucose is produced and can directly enter glycolysis.
In other cases, these sugars are converted into glycolysis intermediates that come later in the pathway. For example, fructose receives a phosphate group to form either fructose 6-phosphate (which can enter glycolysis at step 3) or fructose 1-phosphate (which can be converted into glyceraldehyde 3-phosphate in the liver and enter glycolysis at step 6).
Lipids are a good source of energy because of their chemical structure: they are rich in carbon-carbon and carbon-hydrogen bonds. After a meal, the small intestine absorbs triacylglycerols and either consumes them or stores them in fat tissue. These lipids are broken down inside cells to glycerol and fatty acids. The fatty acids are shortened by β-oxidation, which removes 2-carbon units from their ends.
ATP is not produced in β-oxidation, but instead NADH and FADH2 are produced.
The complete oxidation of palmitic acid, a fatty acid with 16 carbons, produces 106 molecules of ATP. Fatty acids are a good source of energy, but they cannot be used by all cell types (e.g., red blood cells or brain cells).
Regulation of Cellular Respiration
ATP is the key end product of cellular respiration, and it is constantly being broken down and re-synthesized.
The level of ATP in the cell is an indicator of how much energy a cell has available. When ATP levels are high, the cell has a large amount of free energy. In this case, the cell does not need to keep making ATP, so the pathways that generate it are slowed or down-regulated.
When ATP levels are low, the cell activates or up-regulates the pathways that lead to ATP synthesis.
Other intermediates are also used to regulate ATP production. What happens if the cell has high levels of NAD+? (Cellular respiration is stimulated.) What happens if the cell has high levels of NADH? (Cellular respiration is down-regulated.)
How does this regulation work?
One mechanism is to regulate enzymes that control key steps in the cellular respiration pathway.
During glycolysis, step 3, the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate, is an irreversible reaction. It is considered a committed step in the process and is under tight control. This reaction is catalyzed by the enzyme phosphofructokinase-1 (PFK-1).
PFK-1 is an allosteric enzyme with many activators and inhibitors. When levels of ADP or AMP are high in the cell, these molecules will bind to PFK-1 and activate the enzyme so that glycolysis continues, increasing the amount of ATP in the cell. When levels of ATP are high, it will bind to the enzyme, inhibiting its activity and causing glycolysis to slow down.
PFK-1 is also regulated by citrate, an intermediate of the citric acid cycle. When citrate binds to the enzyme, its activity is also slowed.
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